What railroad? Where? Track layout? Not mile marker. Could be some kind of speed limit. Permanent sign or temporary flag type? Need lots more information to determine answer.
Kipling needs help! You gave us who. How and Why are your questions.
WHAT - a trackside sign. Which railroad? Size? Shape? Color? General surroundings?
WHERE? WHEN?
Note that SPRT is not in the AAR listing of railroad reporting marks. Nor does it appear in the Abbreviations.com list of standard abbreviations (except as a river in Peru.) Is it possible that the sign is in a township, designating something important to that township or some other business or political entity, and only coincidentally located next to a track?
Without more, and more specific, information I could spray the ground and sky with semi-educated guesses, with a very low probability of hitting the correct answer.
If we could see a picture of it, know its location and railroad, we could help identify. It could be legitimate railroad fare or it could be something entirely different…we can’t tell unless we know more.
An excellent guess…again, not seeing a picture nor better description or the address for the Ebay listing, we really can’t tell. I had another thought about it being an NJT marker for the Sports Line.
WOW Wan! But from what railroad or transit operation? What location? I am beginning to think SPRT is South (something: Portland, Philadelphia, Peoria, Pittsburgh, P----------?) Rapid Transit perhaps. Definitely transit (or trolley?) than railroad. Numbers could be present (top) and next (bottoms) speed restrictions. Can’t be number of cars spotting because they are too desperate from 1 to 8 to 10 and from 50 to 11. May not even be USA for that matter.